Stroke is the leading cause of long-term disability and third leading cause of death. While most research has focused on acute stroke treatment and neuroprotection, exploiting brain self-repair may provide better therapies. Unfortunately, current experimental therapies including pharmaceuticals, and stem cells may engender significant and unacceptable risks. Here we describe a distinct type of stroke therapy, a naturally occurring extracellular matrix fragment of perlecan, domain V, which functions by being neuroprotective and enhancing the brain's own response to injury. Domain V is well tolerated, specifically targets stroked and peri-infarct brain tissue, can be administered 24 hours after stroke, restores stroke-affected motor function to baseline pre-stroke levels, and exerts its beneficial effect via a previously unreported mechanism of upregulation of and interaction with the α5β1 integrin and subsequent release of vascular endothelial growth factor.
Ischemic stroke, a condition resulting from occlusion of brain vasculature1, manifests as an energy deprived ischemic core of rapid cell death, surrounded by vulnerable regions with less severe energy deprivation (i.e. penumbra)2-4. Within these regions, reparative revascularization (angiogenesis) and neuronal repopulation (neurogenesis) occur in close proximity5-7 affording mutually supportive growth factor-mediated neuron-endothelial cell cross-talk8-11. Additionally, angiogenic blood vessels serve as a physical scaffold for neurons to migrate towards the ischemic core5. Collectively, neurovascular coupling appears to represent an important means of post-stroke brain repair that could be therapeutically exploited12. Indeed, recent experimental stroke therapies, including pharmaceuticals, stem cell replacement therapies, and growth factors have attempted to capitalize on our understanding of emerging neurovascular concepts to promote functional stroke recovery13-17. However, drug and growth factor therapies raise questions of potentially serious systemic side effects, drug interactions, and contra-indications. Similarly, cell-based therapies raise important safety issues of “where do the cells go?” once injected and whether injected cells become undesirable tumors or other abnormal ectopic tissue. Furthermore, growth factors can have vastly different positive or negative consequences for stroke depending on when they are administered relative to the stroke injury. For example, vascular endothelial growth factor (VEGF) may worsen already disrupted blood brain barrier permeability (a hallmark of early stroke pathology) and promote brain edema, as well as enhance hemorrhagic transformation and brain infarct size18 if administered early after stroke onset. However, if the same VEGF is given more chronically post-stroke, it is neuroprotective, enhances angiogenesis and neurogenesis19-21.
Perlecan is required for both angiogenesis and neurogenesis24, and may be neuroprotective due to the sequestration and release of various growth factors. Interestingly, perlecan is also known to harbor an anti-angiogenic C-terminal protein Domain V (DV, also known as endorepellin25) that is activated by proteolysis from full length perlecan22. However, the presence and brain activity of DV have not been characterized due in part to the absence of DV's previously identified anti-angiogenic α5β1 integrin receptor from angiogenic brain endothelial cells25-27.
Using two different stroke models (the rat endothelin-1-induced cerebral ischemia and the mouse middle cerebral artery occlusion MCAo models), a stable and long-lasting increase in brain DV levels following stroke injury has been demonstrated. In addition, post-stroke administered DV is well-tolerated, targets stroke and peri-infarct vasculature, is neuroprotective, unexpectedly enhances brain angiogenesis and significantly improves post-stroke functional motor recovery to pre-stroke baseline function via a previously unidentified receptor and signal transduction pathway. Collectively, the results reveal unexpected differences between brain and nonbrain angiogenesis and demonstrate that DV is a putative, distinct, well tolerated, neurovascular-targeting experimental stroke therapy.